Back incidence type avalanche photodetector and preparation method thereof

Abstract

The invention discloses a back incidence type avalanche photodetector and a preparation method thereof. The technical problems that the detection efficiency of an existing photodetector is difficult to improve, the detection efficiency is too low, the detection wave band is limited, and the process compatibility is poor are solved. The photoelectric detector comprises a substrate layer, a multiplication layer, a space charge layer, an absorption layer, a P contact layer, a passivation region, negative electrode metal and positive electrode metal which are sequentially arranged from bottom to top, wherein the substrate layer is used for entering of incident light, and the positive electrode metal comprises a disc structure and a circular ring structure which are coaxially arranged; wherein the disc structure is located above the passivation region and the diameter of the disc structure is smaller than that of the P contact layer; the outer diameter of the circular ring structure is smaller than the diameter of the disc structure; the lower end of the ring structure is connected with the P contact layer, and the upper end surface is flush with the upper surface of the passivation region and is connected with the bottom of the disc structure. The detection efficiency of the photoelectric detector is obviously improved.

Description

Technical Field

[0001] The invention relates to a single-photon detector, and in particular to a back-incident avalanche photoelectric detector and a preparation method thereof. Background Art

[0002] With the rapid development of information technology, the demand for high-performance infrared optoelectronic devices in the fields of communication and imaging is growing. In this context, silicon-based optoelectronic devices have attracted much attention due to their low cost and compatibility with existing silicon integrated circuit processes. However, silicon has a large bandgap and limited absorption rate in the communication wavelength range, which limits its application in infrared photodetection and light emission. The commonly used III-V photodetector devices are also incompatible with the existing silicon photonic process platform, resulting in high production costs and difficulty in further improving integration.

[0003] To overcome these defects, researchers began to explore the use of germanium photodetectors, which are the same Group IV materials as silicon, to develop new silicon-based germanium photodetector devices. The key to such devices is to use germanium as the absorption layer material, so that the detector can respond to infrared light signals; and silicon as the multiplication layer material, which can "multiply and amplify" weak signal light, thereby meeting the needs of key applications such as quantum communication, vehicle-mounted laser radar, and terrain mapping.

[0004] For example, "Ge-on-Si Single-Photon Avalanche Diode Detectors: Design, Modeling, Fabrication, and Characterization at Wavelengths 1310 and 1550 nm" (IEEE Transactions on Electron Devices, 2013, 60 (11): 3807-3813) published by Warburton RE, Intermite G, Myronov M, et al. discloses a germanium avalanche photodetector, which adopts a positive incidence type, that is, the positive and negative metals and the light incident surface are both on the front of the detector, which will cause part of the incident light to be reflected or refracted, resulting in a small filling factor of the detector's photosensitive surface (the ratio of the detector's photosensitive area area to the detector's overall area), and it is difficult to improve the detection efficiency. At the same time, the presence of metal electrodes will also make it difficult to prepare a super surface structure or a micro lens structure on the detector surface, further limiting the improvement of the detection efficiency.

[0005] A Chinese patent with publication number CN116705873A discloses a back-incident photodetector chip based on a bulk silicon substrate and a method for preparing the same. The back-incident photodetector device uses germanium as the absorption region material but does not adopt an avalanche structure, does not have a carrier multiplication effect, cannot detect weak signal light, and has an excessively low detection efficiency.

[0006] A Chinese patent with publication number CN110993710A discloses a single-photon avalanche diode and a method for preparing the same. The patent discloses a back-incident avalanche photodetector device, but uses silicon as the absorption zone material, so that the detection band is limited by the bandgap width of the silicon material. The responsive band is below 1000nm, and it is unable to detect the 1550nm band light commonly used in various applications such as autonomous driving lidar.

[0007] A Chinese patent with publication number CN117423767A discloses a back-incident avalanche photodetector and a method for making the same. The detector can be used to detect light in the 1550nm band, but the materials used are InP and InGaAs, which are Group III-V materials and cannot be directly integrated with a silicon substrate. The detector has poor compatibility with existing silicon process platforms and has a high production cost. Summary of the invention

[0008] The purpose of the present invention is to solve the technical problems that the detection efficiency of existing forward-incident photodetectors is difficult to improve, the detection efficiency of back-incident photodetectors is too low, the detection band is limited, and the process compatibility is poor, and to provide a back-incident avalanche photodetector and a preparation method thereof.

[0009] To achieve the above object, the technical solution adopted by the present invention is:

[0010] A back-incident avalanche photodetector, which is special in that it includes a substrate layer, a multiplication layer, a space charge layer, an absorption layer, a P contact layer, a passivation region, a negative electrode metal and a positive electrode metal arranged in sequence from bottom to top; wherein the diameter of the P contact layer is less than or equal to the diameter of the absorption layer; the diameter of the absorption layer is greater than or equal to the diameter of the space charge layer and less than or equal to the diameter of the multiplication layer; the diameter of the space charge layer is less than or equal to the diameter of the multiplication layer; the diameter of the multiplication layer is less than the diameter of the substrate layer; the substrate layer is used for the entry of incident light;

[0011] The passivation region is located above the P contact layer and extends downward to cover the P contact layer, the absorption layer, the space charge layer, the multiplication layer, and the upper surface of the substrate layer;

[0012] The negative electrode metal is a ring-shaped structure and is located in the passivation area; the lower end of the negative electrode metal is in contact with the substrate layer, and the upper end extends out of the passivation area for connecting to an external power source;

[0013] The positive electrode metal includes a coaxially arranged disc structure and a ring structure; wherein the disc structure is used to connect to an external power source, is located above the passivation zone and has a diameter smaller than the P contact layer; the ring structure is located in the passivation zone, and has an outer diameter smaller than the diameter of the disc structure; the lower end of the ring structure is connected to the P contact layer, and the upper end surface is flush with the upper surface of the passivation zone and connected to the bottom of the disc structure.

[0014] Furthermore, the substrate layer includes a silicon substrate, a silicon oxide layer and an N contact layer arranged in sequence from bottom to top, or the substrate layer is an N contact layer; the multiplication layer is in contact with the upper surface of the N contact layer, and the lower end of the negative electrode metal is in contact with the upper surface of the N contact layer.

[0015] Furthermore, the material of the N-contact layer is N-type doped Si; the material of the multiplication layer is intrinsic Si; the material of the space charge layer is P-type doped Si or P-type doped Si x Ge 1-x , where 0<x<1; the material of the absorption layer is intrinsic Ge or intrinsic Si x Ge 1-x ; The material of the P contact layer is P-type doped Ge or P-type doped Si x Ge 1-x .

[0016] Further, when the diameter of the P contact layer is equal to the diameter of the absorption layer, the P contact layer covers the upper surface of the absorption layer;

[0017] When the diameter of the P-contact layer is smaller than the diameter of the absorption layer, the P-contact layer covers the upper surface of the absorption layer, or is embedded in the absorption layer and the upper surface is flush with the upper surface of the absorption layer.

[0018] Further, when the diameter of the space charge layer is equal to the diameter of the multiplication layer, the space charge layer covers the upper surface of the multiplication layer;

[0019] When the diameter of the space charge layer is smaller than the diameter of the multiplication layer, the space charge layer covers the upper surface of the multiplication layer, or is embedded in the multiplication layer and the upper surface is flush with the upper surface of the multiplication layer.

[0020] Furthermore, a passivation layer is provided on the lower surface of the substrate layer, and a super surface structure or a micro lens structure is provided on the lower surface of the passivation layer.

[0021] Furthermore, the material of the positive electrode metal and the negative electrode metal is a combination of one or more of Au, Ag, Al, and Pt.

[0022] The present invention also provides a method for preparing a back-incident avalanche photodetector, comprising the following steps:

[0023] Step [1] Prepare a substrate layer, and then form a multiplication layer on the upper surface of the substrate layer by RPCVD process or MBE process;

[0024] Step [2] forming a space charge layer on the upper surface of the multiplication layer by an in-situ doping epitaxy method or an ion implantation method, wherein the diameter of the space charge layer is less than or equal to the diameter of the multiplication layer;

[0025] Step [3] growing an absorption layer on the upper surface of the space charge layer by RPCVD process or MBE process;

[0026] Step [4] forming a P contact layer on the upper surface of the absorption layer by an in-situ doping epitaxy method or an ion implantation method, wherein the diameter of the P contact layer is less than or equal to the diameter of the absorption layer, and the diameter of the absorption layer is less than or equal to the diameter of the multiplication layer;

[0027] Step [5] Based on step [4], an ICP-RIE method is used to etch from top to bottom to form a mesa structure; in the mesa structure, the diameter of the multiplication layer is smaller than the diameter of the substrate layer;

[0028] Step [6] depositing a passivation region covering the P contact layer and the mesa structure etched in step [5] by a CVD process;

[0029] Step [7] etching a negative electrode metal window and a positive electrode metal window in the passivation region using an ICP-RIE process, wherein the lower end of the negative electrode metal window extends to the upper surface of the substrate layer, and the lower end of the positive electrode metal window extends to the upper surface of the P contact layer;

[0030] Step [8] A negative electrode metal and a positive electrode metal are formed on the negative electrode metal window and the positive electrode metal window respectively by electron beam evaporation or magnetron sputtering process, wherein the upper end surface of the positive electrode metal is a disk structure, thereby completing the preparation of a back-incident avalanche photodetector.

[0031] Furthermore, step [8] is specifically to form a negative electrode metal in the negative electrode metal window by electron beam evaporation or magnetron sputtering process, then first form a ring structure of positive electrode metal in the positive electrode metal window, and then form a disk structure on the top of the ring structure, wherein the lower surface of the disk structure is flush with the upper surface of the passivation layer, and is in contact with the upper end of the ring structure; the diameter of the disk structure is greater than or equal to the outer diameter of the ring structure, and less than or equal to the diameter of the P contact layer, thereby completing the preparation of the back-incident avalanche photodetector.

[0032] Compared with the prior art, the present invention has the following beneficial technical effects:

[0033] 1. The present invention forms a back-incident avalanche photodetector by adding a multiplication layer and adopting a back-incident structure in which the detection light is incident from the substrate layer. The avalanche multiplication effect is used to improve the sensitivity of the photodetector, thereby being able to detect weak signal light. At the same time, the upper end of the positive electrode metal is designed to be a disk structure, which can perform secondary reflection on the incident light, thereby increasing the optical path of the incident light in the detector and improving the detection efficiency.

[0034] 2. The lower surface of the substrate layer or passivation layer of the present invention is relatively flat, without other structures such as metal electrodes, which is conducive to the preparation of a super surface structure or a microlens structure on the back of the device, and can further improve the detection efficiency.

[0035] 3. The absorption layer material of the present invention uses intrinsic Ge or Si x Ge 1-x The selection of this material can realize signal detection in the 800-1800nm ​​band, and it is easier to integrate with the readout circuit. It is compatible with the existing silicon photonic process platform and can also reduce the production cost of the device.

[0036] 4. The present invention can prepare back-incident avalanche photodetectors with different table structures. The front side of the device can be interconnected with the control and readout circuits, and the back side light can be incident normally, which is convenient for the application of large-scale detector arrays. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The figure is a schematic structural diagram of an embodiment of a back-incident silicon germanium avalanche photodetector of the present invention.

[0038] Figure 2 The figure is a schematic diagram of a single table structure in an embodiment of a back-incident silicon germanium avalanche photodetector of the present invention.

[0039] Figure 3 It is a schematic diagram of a double-table structure in an embodiment of a back-incident silicon germanium avalanche photodetector of the present invention.

[0040] Figure 4 This is a schematic diagram of the three-table structure in an embodiment of a back-incident silicon germanium avalanche photodetector of the present invention.

[0041] Figure 5 This is a structural schematic diagram of an embodiment of a back-incident silicon germanium avalanche photodetector of the present invention, in which the diameter of the P contact layer is smaller than that of the absorption layer, and the diameter of the space charge layer is equal to that of the multiplication layer.

[0042] Figure 6 It is a structural schematic diagram of an embodiment of a back-incident silicon germanium avalanche photodetector of the present invention, in which the diameter of the P contact layer is equal to that of the absorption layer, and the diameter of the space charge layer is smaller than that of the multiplication layer.

[0043] Figure 7It is a schematic structural diagram of a back-incident silicon germanium avalanche photodetector embodiment of the present invention, in which the diameter of the P contact layer is smaller than that of the absorption layer, and the diameter of the space charge layer is smaller than that of the multiplication layer.

[0044] Figure 8 It is a structural schematic diagram of forming a multiplication layer on the upper surface of a substrate layer in an embodiment of a method for preparing a back-incident silicon germanium avalanche photodetector of the present invention.

[0045] Fig. 9 It is a schematic structural diagram of forming a space charge layer on a multiplication layer in an embodiment of a method for preparing a back-incident silicon germanium avalanche photodetector of the present invention.

[0046] Fig.10 It is a schematic structural diagram of growing an absorption layer on a space charge layer in an embodiment of a method for preparing a back-incident silicon germanium avalanche photodetector of the present invention.

[0047] Fig.11 It is a structural schematic diagram of forming a P contact layer on an absorption layer in an embodiment of a method for preparing a back-incident silicon germanium avalanche photodetector of the present invention.

[0048] Fig.12 The figure is a schematic diagram of the etched mesa structure in an embodiment of a method for preparing a back-incident silicon germanium avalanche photodetector of the present invention.

[0049] Fig.13 The present invention is a schematic structural diagram of a method for preparing a back-incident silicon germanium avalanche photodetector in which a passivation region is deposited.

[0050] Fig.14 The figure is a comparison diagram of the spectral response curves of a back-incident silicon germanium avalanche photodetector and a forward-incident detector of the present invention.

[0051] The reference numerals are as follows:

[0052] 10 - silicon substrate, 20 - silicon oxide layer, 30 - N contact layer, 40 - multiplication layer, 50 - space charge layer, 60 - absorption layer, 70 - P contact layer, 80 - passivation region, 90 - negative electrode metal, 100 - positive electrode metal, 101 - disk structure, 102 - ring structure. DETAILED DESCRIPTION

[0053] In order to make the purpose, advantages and features of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0054] like Figure 1As shown, this embodiment provides a back-incident avalanche photodetector, including a substrate layer, a multiplication layer 40, a space charge layer 50, an absorption layer 60, a P contact layer 70, and a passivation region 80, a negative electrode metal 90 and a positive electrode metal 100, which are arranged in sequence from bottom to top; wherein the diameter of the P contact layer 70 is less than or equal to the diameter of the absorption layer 60; the diameter of the absorption layer 60 is greater than or equal to the diameter of the space charge layer 50 and less than or equal to the diameter of the multiplication layer 40; the diameter of the space charge layer 50 is less than or equal to the diameter of the multiplication layer 40; and the diameter of the multiplication layer 40 is less than the diameter of the substrate layer.

[0055] The substrate layer is used for the entry of incident light, and there is no metal obstruction on the light incident surface of the detector, which improves the filling factor of the detector and further improves the detection efficiency of the detector.

[0056] The passivation region 80 is located above the P-contact layer 70 and extends downward to cover the P-contact layer 70 , the absorption layer 60 , the space charge layer 50 , the multiplication layer 40 , and the upper surface of the substrate layer.

[0057] The negative electrode metal 90 is a ring-shaped structure and is located in the passivation area 80; the lower end of the negative electrode metal 90 is in contact with the substrate layer, and the upper end extends out of the passivation area 80 for connecting to an external power source.

[0058] The positive electrode metal 100 includes a coaxially arranged disc structure 101 and a ring structure 102; wherein the disc structure 101 is used to connect to an external power source, and is located above the passivation zone 80 and has a diameter smaller than the P contact layer 70; the ring structure 102 is located in the passivation zone 80, and has an outer diameter smaller than the diameter of the disc structure 101; the lower end of the ring structure 102 is connected to the P contact layer 70, and the upper end surface is flush with the upper surface of the passivation zone 80 and connected to the bottom of the disc structure 101.

[0059] The photodetector of this embodiment adopts a separated absorption, charge, and multiplication (SACM) structure. When working, the signal light is incident from the bottom (i.e., the substrate layer), and then absorbed by the absorption layer 60 to generate carriers, and enters the multiplication layer 40 again under the action of the electric field, avalanche multiplication occurs, and an electrical signal is generated, thereby realizing the detection of the optical signal.

[0060] At the same time, in this embodiment, the upper end surface of the positive electrode metal 100 is designed as a disk structure, which can not only realize the back-incident of the detection light, but also perform secondary reflection on the incident light, thereby increasing the optical path of the incident light in the detector and improving the detection efficiency.

[0061] The substrate layer can be composed of a silicon substrate 10, a silicon oxide layer 20 and an N-contact layer 30 arranged in sequence from bottom to top, or it can be composed of a single N-contact layer 30; the multiplication layer 40 is in contact with and connected to the upper surface of the N-contact layer 30, and the lower end of the negative electrode metal 90 is in contact with and connected to the upper surface of the N-contact layer 30.

[0062] In order to protect the substrate layer, in this embodiment, an additional passivation layer may be grown on the lower surface of the substrate layer.

[0063] Preferably, since the lower surface of the substrate layer or the passivation layer is relatively flat, a supersurface structure or a microlens structure can be prepared on the lower surface of the substrate layer or the lower surface of the passivation layer, wherein the supersurface structure is a micro-nano hole with a rectangular array and periodic arrangement on the light incident surface, and the microlens structure is a tiny lens array corresponding to the detector pixels one by one for focusing the incident light to enhance the photoelectric detection efficiency. The design of the supersurface structure or the microlens structure can further improve the detection efficiency.

[0064] In this embodiment, the material of the N-contact layer 30 is N-type doped Si; the material of the multiplication layer 40 is intrinsic Si. Using silicon as the multiplication layer material makes the detector have extremely high sensitivity through the avalanche multiplication effect, thereby being able to detect weak light signals.

[0065] The material of the space charge layer 50 is P-type doped Si or P-type doped Si x Ge 1-x , where 0<x<1; the material of the P contact layer 70 is P-type doped Ge or P-type doped Si x Ge 1-x The material of the passivation region 80 is SiO 2 、Si 3 N 4 One or a combination of the two.

[0066] The material of the absorption layer 60 is intrinsic Ge or intrinsic Si x Ge 1-x Compared with the existing technology, it can realize signal detection in the 800-1800nm ​​band. Therefore, Ge and Si are both Group IV materials, which is more convenient for the integration of detection devices and readout circuits. At the same time, it is compatible with the existing silicon photonic process platform and can reduce the device production cost.

[0067] The material of the positive electrode metal 100 and the negative electrode metal 90 may be selected from one or a combination of Au, Ag, Al, and Pt.

[0068] The photodetector of this embodiment forms a mesa structure from bottom to top. Through the ICP-RIE etching process, the mesa structure can be etched into a single-mesa, double-mesa and triple-mesa structure. Intrinsic silicon is used to form a multiplication layer. The avalanche multiplication effect is used to make the device have extremely high sensitivity, thereby realizing the detection of weak light signals.

[0069] Single table structure such as Figure 2As shown, from bottom to top are the N contact layer 30 , the multiplication layer 40 , the space charge layer 50 , the absorption layer 60 , and the P contact layer 70 , wherein the diameters of the multiplication layer 40 , the space charge layer 50 , the absorption layer 60 , and the P contact layer 70 are the same and smaller than the diameter of the N contact layer 30 .

[0070] Double table structure Figure 3 As shown, from bottom to top are the N contact layer 30, the multiplication layer 40, the space charge layer 50, the absorption layer 60, and the P contact layer 70, wherein the diameter of the multiplication layer 40 is smaller than the diameter of the N contact layer 30, and the diameters of the space charge layer 50, the absorption layer 60, and the P contact layer 70 are the same and smaller than the diameter of the multiplication layer 40.

[0071] Three-table structure Figure 4 As shown, from bottom to top are the N contact layer 30, the multiplication layer 40, the space charge layer 50, the absorption layer 60, and the P contact layer 70, wherein the diameter of the multiplication layer 40 is smaller than the diameter of the N contact layer 30, the diameters of the space charge layer 50 and the absorption layer 60 are the same and smaller than the diameter of the multiplication layer 40, and the diameter of the P contact layer 70 is smaller than the diameter of the absorption layer 60.

[0072] The space charge layer 50 and the P contact layer 70 of the device are formed by an ion implantation process. According to the relationship between the diameters of the P contact layer 70 and the absorption layer 60, and the relationship between the diameters of the space charge layer 50 and the multiplication layer 40, the combination can be divided into four cases:

[0073] The first case is Figure 2 As shown, the diameter of the P contact layer 70 is equal to the diameter of the absorption layer 60 , and the diameter of the space charge layer 50 is equal to the diameter of the multiplication layer 40 ; at this time, the P contact layer 70 covers the upper surface of the absorption layer 60 , and the space charge layer 50 covers the upper surface of the multiplication layer 40 .

[0074] The second case is Figure 5 As shown, the diameter of the P contact layer 70 is smaller than the diameter of the absorption layer 60, and the diameter of the space charge layer 50 is equal to the diameter of the multiplication layer 40; at this time, the P contact layer 70 is embedded in the absorption layer 60 and the upper surface is flush with the upper surface of the absorption layer 60, and the space charge layer 50 covers the upper surface of the multiplication layer 40.

[0075] The third situation is Figure 6 As shown, the diameter of the P contact layer 70 is equal to the diameter of the absorption layer 60, and the diameter of the space charge layer 50 is smaller than the diameter of the multiplication layer 40; at this time, the P contact layer 70 covers the upper surface of the absorption layer 60, and the space charge layer 50 is embedded in the multiplication layer 40 and the upper surface is flush with the upper surface of the multiplication layer 40.

[0076] The fourth case is Figure 7As shown, the diameter of the P contact layer 70 is smaller than the diameter of the absorption layer 60, and the diameter of the space charge layer 50 is smaller than the diameter of the multiplication layer 40; at this time, the P contact layer 70 is embedded in the absorption layer 60 and the upper surface is flush with the upper surface of the absorption layer 60, and the space charge layer 50 is embedded in the multiplication layer 40 and the upper surface is flush with the upper surface of the multiplication layer 40.

[0077] In summary, this embodiment adopts a back-incident mesa structure, using Ge or Si x Ge 1-x As the absorption zone material, the device absorbs infrared light, and uses silicon as the substrate and multiplication zone material. The specific measures are: using a single-table, double-table, or triple-table separated absorption, charge, and multiplication (SACM) structure, using intrinsic silicon to form the multiplication layer, and through the avalanche multiplication effect, the device has extremely high sensitivity and can detect weak light signals; using Ge or Si x Ge 1-x As the absorption zone material, the device has the ability to respond to infrared light; the back-incident structure with same-side and different-side electrodes is used to facilitate the three-dimensional integration of the device with the readout and control circuits, and ultimately a highly integrated and highly detected infrared photodetector can be realized.

[0078] This embodiment also provides a method for preparing a back-incident avalanche photodetector, comprising the following steps:

[0079] Step [1] Figure 8 As shown, a substrate layer is prepared, and then a multiplication layer 40 is formed on the upper surface of the substrate layer by RPCVD (reduced pressure chemical vapor deposition) process or MBE (molecular beam epitaxy) process. Generally, silicon-silicon oxide-silicon is selected as the substrate, and an N contact layer 30 is formed by ion implantation.

[0080] Step【2】 Fig. 9 As shown, a space charge layer 50 is formed on the upper surface of the multiplication layer 40 by an in-situ doping epitaxy method or an ion implantation method, wherein the diameter of the space charge layer 50 is smaller than or equal to the diameter of the multiplication layer 40 .

[0081] Step【3】 Fig.10 As shown, the absorption layer 60 is grown on the upper surface of the space charge layer 50 by RPCVD process or MBE process.

[0082] Step [4] Fig.11 As shown, a P contact layer 70 is formed on the upper surface of the absorption layer 60 by an in-situ doping epitaxy method or an ion implantation method, wherein the diameter of the P contact layer 70 is less than or equal to the diameter of the absorption layer 60 .

[0083] Step [5] Fig.12As shown, on the basis of step [4], ICP-RIE (inductively coupled plasma reactive anisotropic etching) is used to etch from top to bottom to form the following Figure 2 , Figure 3 or Figure 4 In the mesa structure, the diameter of the multiplication layer 40 is smaller than the diameter of the substrate layer, and the diameter of the absorption layer 60 is smaller than or equal to the diameter of the multiplication layer 40 .

[0084] Step [6] Fig.13 As shown, a passivation region 80 covering the P contact layer 70 and the mesa structure etched in step [5] is deposited by a CVD (chemical vapor deposition) process.

[0085] Step [7] The negative electrode metal window and the positive electrode metal window are respectively etched in the passivation region 80 by ICP-RIE process, wherein the negative electrode metal window is a circular ring structure, the lower end of which extends to the upper surface of the substrate layer, and the inner diameter is larger than the inner diameter of the lower end of the passivation region 80, and the outer diameter is smaller than the outer diameter of the lower end of the passivation region 80. The positive electrode metal window is also a circular ring structure, the lower end of which extends to the upper surface of the P contact layer 70, and the outer diameter of the ring is equal to or smaller than the diameter of the P contact layer 70.

[0086] Step [8] A negative electrode metal 90 is formed in the negative electrode metal window by electron beam evaporation or magnetron sputtering process, and then a ring structure 102 of the positive electrode metal 100 is first formed in the positive electrode metal window, and then a disk structure 101 is formed on the top of the ring structure 102, wherein the lower surface of the disk structure 101 is flush with the upper surface of the passivation layer 80 and is in contact with the upper end of the ring structure 102; the diameter of the disk structure 101 is greater than or equal to the outer diameter of the ring structure 102 and less than or equal to the diameter of the P contact layer 70, thereby completing the preparation of the back-incident avalanche photodetector.

[0087] In addition, the lower surface of the substrate layer or the passivation layer may be prepared on the lower surface of the substrate layer or the passivation layer as required, so that the detection efficiency of the detector is further improved.

[0088] like Fig.14 As shown in the figure, the simulation results of the detection device with the same device structure and different light incident modes are obtained by using TCAD simulation software. Under the same incident light intensity, the wavelength of the incident light is changed to obtain the spectral response curves of the back-incident and front-incident devices. It can be seen from the figure that compared with the front-incident detection device, the spectral response of the back-incident detection device at a wavelength of 1310nm increases by 20%, and increases by 13% at 1550nm. It can be concluded that at the commonly used infrared bands of 1310nm and 1550nm, the spectral response performance of the back-incident detection device with the same structure is better than that of the front-incident detection device.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present invention.

Claims

1. A back-incident avalanche photodetector, characterized in that: The invention comprises a substrate layer, a multiplication layer (40), a space charge layer (50), an absorption layer (60), a P contact layer (70), a passivation region (80), a negative electrode metal (90) and a positive electrode metal (100) arranged in sequence from bottom to top; wherein the diameter of the P contact layer (70) is less than or equal to the diameter of the absorption layer (60); the diameter of the absorption layer (60) is greater than or equal to the diameter of the space charge layer (50) and less than or equal to the diameter of the multiplication layer (40); the diameter of the space charge layer (50) is less than or equal to the diameter of the multiplication layer (40); the diameter of the multiplication layer (40) is less than the diameter of the substrate layer; and the substrate layer is used for the entry of incident light; The passivation region (80) is located above the P contact layer (70) and extends downward to cover the P contact layer (70), the absorption layer (60), the space charge layer (50), the multiplication layer (40), and the upper surface of the substrate layer; The negative electrode metal (90) is a ring-shaped structure and is located in the passivation area (80); the lower end of the negative electrode metal (90) is in contact with the substrate layer, and the upper end extends out of the passivation area (80) for connecting to an external power source; The positive electrode metal (100) comprises a coaxially arranged disc structure (101) and a ring structure (102); wherein the disc structure (101) is used to connect to an external power source, is located above the passivation zone (80) and has a diameter smaller than the P contact layer (70); the ring structure (102) is located in the passivation zone (80) and has an outer diameter smaller than the diameter of the disc structure (101); the lower end of the ring structure (102) is connected to the P contact layer (70), and the upper end surface is flush with the upper surface of the passivation zone (80) and is connected to the bottom of the disc structure (101).

2. The back-incident avalanche photodetector according to claim 1, characterized in that: The substrate layer comprises a silicon substrate (10), a silicon oxide layer (20) and an N contact layer (30) which are arranged in sequence from bottom to top, or the substrate layer is the N contact layer (30); The multiplication layer (40) is in contact with and connected to the upper surface of the N contact layer (30), and the lower end of the negative electrode metal (90) is in contact with and connected to the upper surface of the N contact layer (30).

3. The back-incident avalanche photodetector according to claim 2, characterized in that: The material of the N-contact layer (30) is N-type doped Si; the material of the multiplication layer (40) is intrinsic Si; the material of the space charge layer (50) is P-type doped Si or P-type doped Si x Ge 1-x , wherein 0<x<1; the material of the absorption layer (60) is intrinsic Ge or intrinsic Si x Ge 1-x The material of the P contact layer (70) is P-type doped Ge or P-type doped Si x Ge 1-x .

4. The back-incident avalanche photodetector according to claim 1, 2 or 3, characterized in that: When the diameter of the P contact layer (70) is equal to the diameter of the absorption layer (60), the P contact layer (70) covers the upper surface of the absorption layer (60); When the diameter of the P contact layer (70) is smaller than the diameter of the absorption layer (60), the P contact layer (70) covers the upper surface of the absorption layer (60), or is embedded in the absorption layer (60) and the upper surface is flush with the upper surface of the absorption layer (60).

5. The back-incident avalanche photodetector according to claim 1, 2 or 3, characterized in that: When the diameter of the space charge layer (50) is equal to the diameter of the multiplication layer (40), the space charge layer (50) covers the upper surface of the multiplication layer (40); When the diameter of the space charge layer (50) is smaller than the diameter of the multiplication layer (40), the space charge layer (50) covers the upper surface of the multiplication layer (40), or is embedded in the multiplication layer (40) and the upper surface is flush with the upper surface of the multiplication layer (40).

6. The back-incident avalanche photodetector according to claim 1, characterized in that: A passivation layer is provided on the lower surface of the substrate layer, and a super surface structure or a micro lens structure is provided on the lower surface of the passivation layer.

7. The back-incident avalanche photodetector according to claim 6, characterized in that: The material of the positive electrode metal (100) and the negative electrode metal (90) is a combination of one or more of Au, Ag, Al and Pt.

8. A method for preparing a back-incident avalanche photodetector according to any one of claims 1 to 7, characterized in that: The following steps are involved: Step [1] Prepare a substrate layer, and then form a multiplication layer (40) on the upper surface of the substrate layer by RPCVD process or MBE process; Step [2] forming a space charge layer (50) on the upper surface of the multiplication layer (40) by an in-situ doping epitaxy method or an ion implantation method, wherein the diameter of the space charge layer (50) is less than or equal to the diameter of the multiplication layer (40); Step [3] growing an absorption layer (60) on the upper surface of the space charge layer (50) by RPCVD process or MBE process; Step [4] forming a P contact layer (70) on the upper surface of the absorption layer (60) by an in-situ doping epitaxy method or an ion implantation method, wherein the diameter of the P contact layer (70) is less than or equal to the diameter of the absorption layer (60); Step [5] Based on step [4], an ICP-RIE method is used to etch from top to bottom to form a mesa structure; in the mesa structure, the diameter of the multiplication layer (40) is smaller than the diameter of the substrate layer, and the diameter of the absorption layer (60) is smaller than or equal to the diameter of the multiplication layer (40); Step [6] depositing a passivation region (80) covering the P contact layer (70) and the mesa structure etched in step [5] by a CVD process; Step [7] using an ICP-RIE process to etch a negative electrode metal window and a positive electrode metal window in the passivation region (80), wherein the lower end of the negative electrode metal window extends to the upper surface of the substrate layer, and the lower end of the positive electrode metal window extends to the upper surface of the P contact layer (70); Step [8] A negative electrode metal (90) and a positive electrode metal (100) are formed on the negative electrode metal window and the positive electrode metal window respectively by electron beam evaporation or magnetron sputtering process, wherein the upper end surface of the positive electrode metal (100) is a disk structure (101), thereby completing the preparation of a back-incident avalanche photodetector.

9. The method for preparing a back-incident avalanche photodetector according to claim 8, characterized in that: Step [8] specifically comprises forming a negative electrode metal (90) in the negative electrode metal window by electron beam evaporation or magnetron sputtering process, then forming a circular ring structure (102) of the positive electrode metal (100) in the positive electrode metal window, and then forming a disk structure (101) on the top of the circular ring structure (102), wherein the lower surface of the disk structure (101) is flush with the upper surface of the passivation layer (80) and is in contact with the upper end of the circular ring structure (102); The diameter of the disk structure (101) is greater than or equal to the outer diameter of the ring structure (102) and less than or equal to the diameter of the P contact layer (70), thereby completing the preparation of the back-incident avalanche photodetector.

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